The incorporation of a shaving aid element in a disposable razor is often desirable. U.S. Pat. No. 4,170,821 ("'821 patent") discloses a razor cartridge with a solid water-soluble shaving aid. The shaving aid can be a lubricant, whisker softener, razor cleaner, medicinal agent, aloe vera, vitamin E, lanolin, and other ingredients or any combination of these. A typical composition of a shaving aid element comprises a hydrophilic polymer and other soluble shaving aids such as those listed above being embedded in a matrix of a hydrophobic polymer. Typically, polyethylene oxide is used as the hydrophilic polymer and polystyrene is used as the hydrophobic polymer. Other compositions are also possible.
Regardless of the exact chemical composition used for the shaving aid element, injection molding or extrusion can be used to manufacture shaving aid elements in quantities necessary for mass production. In injection molding, the shaving aid element is co-molded directly in the razor as shown in U.S. Pat. No. 4,778,640. In extrusion, the shaving aid element is extruded in the desired shape and then typically cut to size as shown in U.S. Pat. No. 4,624,051 ("'051 patent"). Furthermore, positioning the pre-cut elements in the proper orientation and position for affixing to the razor complicates the manufacturing process.
Methods for securing the pre-cut shaving aid element to the razor include mechanical means and adhesives. When mechanical means is utilized, the razor is made with an internal cavity and the shaving aid element is inserted into the cavity as illustrated in the '051 patent. A tab or any like member retains the shaving aid element in the cavity. Disadvantages associated with this method include the need to precisely pre-cut the shaving aid element to close tolerances, as well as the added manufacturing expense and time of producing the tabs or like members.
When an adhesive, such as an acrylate adhesive, is used, the shaving aid element and the razor must be properly positioned after the adhesive is applied and clamped together for a period of time to allow a bond to form. Although the curing time can be reduced by the application of energy, such as ultraviolet radiation, this adds another manufacturing step and increases production costs. Furthermore, the ultraviolet radiation may be absorbed or deflected by structural elements on the razor units, thereby preventing uniform curing of the adhesive. In any event, even an accelerated cure time decreases manufacturing efficiency. Other disadvantages with adhesives are the added expense of the adhesive and the difficulties associated with the handling of adhesives.
The application of ultrasonic energy to join plastic components has been utilized in many industries. In ultrasonic welding, a solid-state power supply transforms electrical energy to 20 kHz or 40 kHz mechanical energy. A converter changes this electrical energy into ultrasonic mechanical vibratory energy. A horn transmits the ultrasonic mechanical energy directly to the parts to be assembled. A combination of applied force, surface friction, and intermolecular friction at the mating surface between the parts to be joined elevates the temperature until the melting point of the material is reached. Force is maintained after the vibrations cease and a molecular bond or weld at the interface is produced. A more complete discussion of ultrasonic welding is found in the following publications, which are hereby incorporated by reference: "Ultrasonics & Microprocessors Team-up for Efficient Assembly", Assembly Engineering, Nov. 1987, and Ultrasonics Plastics Assembly, 1979, published by the Branson Ultrasonics Corporation.
Ultrasonic welding has also been used in the shaving industry. For example, U.S. Pat. No. 5,070,613 describes a razor blade unit with a blade holder secured by a fixation strip ultrasonically welded to a lower portion of the razor blade unit. Further, it is well-known to ultrasonically weld a head portion of a disposable razor to a handle portion. However, ultrasonic welding of a shaving aid element has not been suggested or disclosed in the art.
Thus, there exists a need for a feasible method in which a shaving aid element is ultrasonically welded to a razor.